The present invention is generally directed to cantilevered structural supports, such as guardrail structural systems designed for predominately lateral loadings imposed by impacting vehicles or other sources, such as snow-plowing operations, and specifically to highway guardrail systems made from sheet metal.
Design of structures where lateral forces predominate are encountered in structural systems such as highway guardrail systems and sheet-piling. In these cases, use of hot-rolled steel structural shapes is the prior art. However, in general, cold-form structural shapes from sheet steel provides for lesser cost per pound of material. Design using sheet steel is limited, however, due to readily available thicknesses which tend to be relatively thin when compared to thicknesses vailable from hot-rolled steel structural shape sources.
Fabricating structures designed for lateral loads usually requires fabrication methods that included welding. Government agencies and engineering design firms usually put such significant welding activities under quality-control requirements, such as fabrication shop""s certification, individual welding employee certifications, welding equipment checks and certifications, limits on the types and specifications of steel to be welded and post-fabrication testing of weldments and heat-zone base metal.
The prior art guardrail system uses a standard W6xc3x978xc2xd wide-flange steel beam as a highway guardrail post. Focusing on the strong-post, blocked-out W-beam Systems""s post component, the standard W-beam post consists of a hot-rolled, wide-flange steel beam with a designation of xe2x80x9cW6xc3x978xc2xdxe2x80x9d. This W6xc3x978xc2xd post is punched (usually 7 xe2x80x3 from the post""s top to receive a post-thru-bolt, also known as the thru-bolt, post-bolt, block-bolt, railbolt or carriage-bolt. The post-bolt is the structural connection between and attaching the guardrail systems""s horizontal rail component, thru the spacer-block, to the post component. After punching, the W6xc3x978xc2xd post is usually hotdipped galvanized. The usual post length is 6 foot, due in part to concerns about installation site soil-matrix conditions. The usual post spacing along the horizontal rail component, center-to-center, is 6xe2x80x2-3xe2x80x3. The typical steel grade requirement is 36 ksi.
The prior art use of the standard wide-flange steel beams of constant cross-section leads to material inefficiency, since the design loads in a strong post cantilevered moment resistive application would not require a constant cross-section, and therefore, constant sectional moduli structural properties.
The prior art strong-post highway guardrail lateral structural support system, also known as strong-post W-beam, is engineered to resist deflection primarily via the post and block components. While the W-beam rail component can act to bridge loads to the nearby post/block structural sub-system by way of beam-action, the prior art W-beam, when loaded to design capacity, quickly deflects and goes into a tension-state much like a span-wire or cable.
On impact with a vehicle, the W-beam, at the point of impact, xe2x80x9chingesxe2x80x9d. The W-beam sections up-stream from the impact point are put into tension. The W-beam sections down-stream from the impact point are, initially loaded axially. As the impacting vehicle deflects or pushes the guardrail system back from its original line (vertical plane), the W-beam sections nearby are also put into some bending.
The W-beam rail component was institutionalized by State and Federal Transportation agencies in 1956-1957. In addition to the other concerns addressed, the evolved construction and design concepts of present day vehicles vis-a-vis the pre-1956 passenger-vehicles has not been reflected in the standard Strong-Post guardrail systems. Pre-1956 passenger vehicles tended to be xe2x80x9chard-shelledxe2x80x9d. That is, they were designed, in general, to be rigid boxes with wheels. As such, relatively less stiff crash barriers were designed so as to absorb impacts. The patents for crash barriers pre-1990, in general, discuss providing the shock-absorbing barrier.
Present day passenger vehicles tend to reflect the design concept that the passenger compartment be rigid with the rest of the vehicle sacrificial, that is, crash-able and impact shock-absorbing. Unfortunately, the present day passenger vehicle with the collapsible, shock absorbing front fenders and bumpers, when impacting a standard W-beam, can act to xe2x80x9crampxe2x80x9d the vehicle either up-and-over or down-and-under the W-beam rail until the rigid-structural-components of the passenger compartment engages the rail component. This condition potentially results in pieces of the vehicle""s fender and/or bumper protruding past the vertical plane of the W-beam rail and snagging on the post even in low impacts where the guardrail is still upright (not laidback as a result of a high-energy impact or weak soil foundation conditions).
The present invention""s rail component addresses present passenger vehicle design resulting in greater safety.
The present invention provides a guardrail system made from sheet metal that addresses the shortcomings of the prior art hot-rolled steel structures.
It is an object of the present invention to provide a post component for cantilevered structural support systems subjected principally to lateral-load conditions, such as guardrail systems, which is more economical to fabricate, transport and/or install than prior art cold rolled wide flange beams.
It is further an object of this invention to provide a post component for cantilevered structural support systems subjected principally to lateral-load conditions, such as guardrail, systems, which is lower cost in maintenance than prior art hot rolled wide flange beams.
It is another object of the present invention to provide a block or spacer component for cantilevered structural support systems subjected principally to lateral-load conditions, such as guardrail systems, which is more economical to fabricate, transport than prior art spacer blocks.
It is a further object of the present invention to provide a block or spacer component for cantilevered structural support systems subjected principally to lateral-load conditions, such as guardrail systems, which is lower cost in maintenance than prior art spacer blocks.
It is still another object of the present invention to provide a spacer component with a structural shape that will structurally yield elastically (without permanent deformation) in the horizontal to assure a more full system response to an impacting object. That is, the present inventions""s spacer provides for transfer of force, due to an impacting object, to the next rail element without full development of the post element that the spacer is attached to. This provides for a more system-wide loading and a xe2x80x9csofterxe2x80x9d load regiment for the post in question versus the prior art localized loading.
It is an additional object of the present invention to provide a rail component for cantilevered structural support systems subjected principally to lateral-load conditions, such as guardrail systems, which is more economical to fabricate, transport and install than prior art rails.
It is an object of the present invention to reduce the generation of scrap material from crashed guardrail systems due to vehicle accidents, resulting in lower economic and/or environmental costs from vehicle accidents.
It is a further object of the present invention to provide individual structural components which may be used interchangeably with existing strong-post guardrail systems. That is, the present invention""s post, spacer and rail components may be used with corresponding existing strong-post components.
In summary, the present invention provides a highway guardrail system comprising a plurality of posts; a plurality of spacers attached to respective posts; and a rail attached to the spacers. The post comprises a tube formed from sheet material, including overlapping portions facing toward the highway when installed; and a plurality of connectors to join said overlapping portions together. The spacer comprises a member formed from sheet metal blank including a rail attachment portion, a post attachment portion and a bridge portion connecting said rail and post attachment portions. The rail attachment portions and the bridge portion form an acute angle in plan view; and the bridge portion is tapered from wide to narrow toward the post attachment portion. The rail is tubular formed from sheet metal, including a U-shaped member and a sheet metal plate both having overlapping portions; and a plurality of connectors to join said overlapping portions together.
These and other objects of the present invention will become apparent from the following detailed description.